In a double-tube oscillation damper, the working chambers within the cylinder contain a damping liquid. The annular space between the cylinder and an external container contains both a liquid and a body of gas. The body of gas may be under superatmospheric pressure. A bottom valve unit is provided between the lower working chamber within the cylinder and the body of liquid within the annular space. The liquid within the cylinder should be free of gas and more particularly air enclosures. However, air can enter into the working chambers, e.g. through the bottom valve unit. This air can escape from the upper working chamber through the piston rod guiding and sealing unit. It is desirable to return this air through the piston rod guiding and sealing unit into the annular space. Therefore, a pressure relief valve is provided between a leakage gas collecting means adjacent the piston rod guiding and sealing unit and the annular space confined between the cylinder and the container.